Flashcards in Session 10 - Drugs Rate and Rhythm Deck (62)
What is the cardiac resting membrane potential?
What sets the resting membrane potential for cardiac cells?
The relative permeability of the cardiac myocyte to K+
What is the equilibrium potential of K+?
Outline a contraction of a ventricular myocyte?
o In diastole, the resting membrane potential of cardiac cells is close to the equilibrium potential of K+ (4).
o Initial depolarisation due to spread of electrical activity from pacemaker cells. Once threshold has been reached, fast voltage gated sodium channels are opened, causing depolarisation towards Na+’s equilibrium potential (0).
o Following the rapid depolarisation, a brief repolarisation caused by the outward flow of K+ returns the membrane potential to ~0. (1)
o Na+ channels deactivate, but the depolarisation causes the opening of voltage gated Ca2+ channels, which take longer to activate, keeping the membrane depolarised (2).
o Influx of Ca2+ causes the release of further Ca2+ from cellular stores, causing contraction (See M&R Session 5).
o After ~250ms, Ca2+ channels close.
o Efflux of K+ returns membrane potential to resting (3).
Give the classification of anti-arythmic drugs
Class 1 - Na+ blockes
Class 2 - B blocekrs
Class 3 - K+ channel blockers
Class 4 - Ca2+ channel blockers
Give three types of Na+ channel blockers
Give a type of beta blocker
Give a widely used K+ channel blocker
Give a Ca2+ channel blocker
What are the effects of Flecainide and Lidocaine?
Decrease conduction velocity
Increase depolarisation threshold
What is the route of administration of flecainide?
Oral and intravenous
What are the indications for flecinaide?
Supraventricular tachyarrythmias (atrial arrhythmia)
Give two contraindications for Flecainide?
Heart failure, History of MI
What is the mechanism of action for Flecainide?
Blocks fast, inward Na+ ion channel (Phase 0)
Give three adverse reactions of flecainide
Dizziness, visual disturbances, arrhythmias
What are the drug-drug interactions for Flecainide?
Metabolised by CYP2D6 and eliminated renally. Inducers/inhibitors
How is lidocaine adminstered?
What are the indications for lidocaine?
Ventricular arrhythmias following MIO
What are the contraindications for Lidocaine (2)
Give three adverse drug reactions for lidocaine
What do beta blockers act on?
B1 receptors in the heart
What is the action of B blockers
Block sympathetic action
Decrease slop of pacemaker potential in SAN
Inhibits adenyl cyclase, decrease inotrophy
What do B blockers do to ventricular action potential?
Shifts it to the right
What are the indications for B blockers? (4)
Post myocardial infarction
What are the two main contraindications for beta blockers?
General decreased heart function
What is the mechanism of action for beta blockers?
Antagonise β-adrenoreceptors. β1-receptors are found in the heart, when they are activated they cause increased Chronotropy and Inotropy.
Inhibits renin release
Give some adverse drug reactions for beta blockers
Bronchospasm, fatigue and insomnia, dizziness, cold extremities, hypotension, bradycardia and decreased glucose tolerance in diabetic patients – Don’t feel adrenaline from hypoglycaemia due to B blockers, dangerous
Give two drug-drug interactions of Beta blockers
Prevents Salbutamol working (β2-adrenoagonist)
Verapamil – Both have –‘ve inotropic action
What do K+ channel blockers do?
Prolong the absolute refractory period by increase AP duration
Also suppress re-entry circuits by closing excitable gap
Why are they not generally used?
Torsades de pointes
Give an example of a potassium channel blocker
What is the route of administration of potassium channel blockers?
Oral or intravenous
What are the indications for potassium channel blockers
Ventricular and supraventricular arrythmia
What are some drug-drug interactions of amiodarone?
Inhibits CYP3A4, CYP2C9 and P-glycoprotein
Dose reductions of Warfarin, Digoxin, Flecainide needed
What do Ca2+ blockers do?
Increased refractory period
Decreased Chronotrophy and Inotropy
Give two examples of Calcium channel blockers
Give a route of admin for calcium
Give three indications for Ca2+ blockers
Prophylaxis and treatment of angina nad hypertension
Give three contraindications for Calcium channel blockers
AV node block
Give four adverse reactions to calcium channel blockers?
What is used to treat torsades de pointes?
What does adenosine do?
Blocks AV node
What are the two main effects of adenosine?
Increased AVN refractory period
What are two main indications for digoxin?
Supraventricular arrhythmias, Heart Failure
Give two contraindications for digoxin
Outline the mech of action of digoxin
o Inhibits Na/K-ATPase
o Direct Cardiac Effects
Inotrope – Used in heart failure, no mortality benefit
o CNS Effects
Sensitises baroreceptor reflex
o Combined Effects
Automaticity of SAN and AVN
AVN refractory period
Conduction velocity of AVN
What are three adverse drug reactions to digoxin?
o Narrow therapeutic index
o Toxicity enhanced with hypokalaemia
o Cardiac toxicity – bradycardia, AVN block, atrial tachycardia
Give some drugs which increase digoxin levels
Popafenone, Quinidine, Amiodarone, Verapamil, Spironolactone, Cylosporine
Give some drugs which decrease digoxin levels
Erythromycin, Tetracycline (gut bacteria metabolise digoxin)
Why do you split loading dose of digoxin in two?
To minimise toxicity risk
How much of digoxin is protein bound
What is digoxin clearance proportional to?
Give three examples of ACE inhibitors
Give three indications for ACE inhibitors
Give three contraindications for ACE inhibitors
Outline mech of action of ACE inhibitors
ACE inhibitors cause inhibition of Angiotensin Converting Enzyme, consequently reducing Angiotensin II and Aldosterone levels. This causes vasodilation and consequent reduction in peripheral resistance and reduced sodium retention.
Reduce breakdown of the vasodilator Bradykinin
Give five adverse reactions of ACE inhibitors
Characteristic dry cough
Angio-oedema (rare, but more common in black population)
Hypotension, dizziness and headache, diarrhoea and muscle cramps
Give two angiotensin blockers
What is an indication for angiotensin blocker?
Give four contraindications
Caution in renal artery stenosis and aortic stenosis
What is the mech of action of angiotensin blocker?
Bind to and antagonise the receptor for Angiotensin II – Angiotensin 1 Receptor (AT1 R).
Inhibits vasoconstriction and aldosterone stimulation by angiotensin II.